The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In FIG. 1, a functional block diagram of a refrigeration system is presented. The refrigeration system includes a compressor 102, a condenser 104, an expansion valve 106, and an evaporator 108. The compressor 102 receives refrigerant in vapor form and compresses the refrigerant, providing pressurized refrigerant in vapor form to the condenser 104. The compressor 102 includes an electric motor and may be a scroll compressor or a reciprocating compressor.
All or a portion of the pressurized refrigerant is converted into liquid form within the condenser 104. The condenser 104 transfers heat away from the refrigerant, thereby cooling the refrigerant. When the refrigerant vapor is cooled to a temperature that is less than a saturation temperature, the refrigerant transforms into a liquid (or liquefied) refrigerant. The condenser 104 may include an electric fan that increases the rate of heat transfer away from the refrigerant.
The condenser 104 provides the refrigerant to the evaporator 108 via the expansion valve 106. The expansion valve 106 controls the flow rate at which the refrigerant is supplied to the evaporator 108. The expansion valve 106 may include a thermostatic expansion valve or may be controlled electronically by, for example, a system controller 130. A pressure drop caused by the expansion valve 106 may cause a portion of the liquefied refrigerant to transform back into the vapor form. In this manner, the evaporator 108 may receive a mixture of refrigerant vapor and liquefied refrigerant.
The refrigerant absorbs heat in the evaporator 108. Liquid refrigerant transitions into vapor form when warmed to a temperature that is greater than the saturation temperature of the refrigerant. The evaporator 108 may include an electric fan that increases the rate of heat transfer to the refrigerant. The heat is removed from air flowing across the evaporator 108 and the resulting cooled air is circulated through the building.
A utility 120 provides power to the refrigeration system. For example only, the utility 120 may provide single-phase alternating current (AC) power at approximately 230 Volts (V) root mean squared (RMS) or at another suitable voltage. In various implementations, the utility 120 may provide three-phase power at approximately 400 Volts RMS or 480 Volts RMS at a line frequency of, for example, 50 or 60 Hz. The utility 120 may provide the AC power to the system controller 130 via an AC line. The AC power may also be provided to a drive controller 132 via the AC line. In other implementations, the utility 120 may supply direct current (DC) power.
The system controller 130 controls the refrigeration system. For example only, the system controller 130 may control the refrigeration system based on user inputs and/or parameters measured by various sensors (not shown). The sensors may include pressure sensors, temperature sensors, current sensors, voltage sensors, etc. The sensors may also include feedback information from the drive controller 132, such as motor currents or torque, over a serial data bus or other suitable data bus.
A user interface 134 provides user inputs to the system controller 130. The user interface 134 may additionally or alternatively provide the user inputs to the drive controller 132. The user inputs may include, for example, a desired temperature, requests regarding operation of a fan (e.g., the evaporator fan), and/or other suitable inputs. The system controller 130 may control operation of the fan of the condenser 104, the fan of the evaporator 108, and/or the expansion valve 106. In various implementations, the drive controller 132 may instead control the condenser fan.
The drive controller 132 may control the compressor 102 based on commands from the system controller 130. For example only, the system controller 130 may instruct the drive controller 132 to operate the compressor motor at a certain speed.
In FIG. 2, a simplified schematic of the drive controller 132 is shown. The drive controller 132 includes control logic 200 that controls a drive circuit 204. The drive circuit 204 produces potentials and currents on phases of a motor 208 of the compressor 102. The motor 208 includes first, second and third windings 212-1, 212-2, and 212-3, referred to as windings A, B, and C, respectively. Although pictured in a Y configuration, the motor 208 may also be wired using a delta configuration.
The drive circuit 204 includes an input bridge 220, which converts incoming AC voltage into a DC voltage output on a DC bus 224. The DC bus 224 powers an inverter stage 228, which switches the DC bus to apply potentials to the windings 212 of the motor 208. The input bridge 220 in this example includes rectifying diodes 232-1, 232-2, and 232-3, as well as rectifying diodes 236-1, 236-2, and 236-3. In this example, the incoming AC power is 3-phase and therefore 3 pairs of rectifying diodes are used. In other implementations, the input bridge 220 may include a controlled rectifier.
The DC bus 224 may include one or more capacitors 240 to remove voltage ripple. While not shown in this example, the input bridge 220 may also include power factor correction components that actively and/or passively improve the power factor of the input bridge 220.
Additional components 244 for inrush limiting and inductance may be present. Inrush limiting may include a resistor that can be bypassed during normal operation. During startup, the resistor is not bypassed and therefore reduces the amount of current being pulled from the AC line when the capacitor 240 is first being charged. An inductor placed in series may also limit inrush current and may be configured not to be bypassed so that the inductor can limit fault current during normal operation. In addition, the inductor may smooth the voltage of the DC bus 224. Additionally, or alternatively, inrush control may be implemented in the positive line 224 or may be implemented between the 3-phase AC line and the input bridge 220.
The inverter stage 228 includes switches 250-1, 250-2, 250-3, 254-1, 254-2, and 254-3. There are three pairs of switches 250 and 254, with each pair corresponding to one of the motor windings 212. The node at the connection point of each pair of switches 250 and 254 is attached to a corresponding one of the motor windings 212. The switches 250 and 254 may include transistors and in some implementations may be insulated gate bipolar junction transistors (IGBTs). As shown, the switches 250 and 254 may be N channel, but in other implementations are P channel or a combination of both N channel and P channel. Across each of the switches 250 and 254 is a diode connected anti-parallel. Specifically, diodes 258-1, 258-2, 258-3, 262-1, 262-2, and 262-3 are connected to the switches 250-1, 250-2, 250-3, 254-1, 254-2, and 254-3, respectively. In various implementations, anti-parallel diodes may be included within a single package with one or more IGBTs.
Control terminals of the switches 250 and 254 are manipulated by the control logic 200. The control logic 200 interfaces with the system controller 130 of FIG. 1. The control logic 200 may also measure currents and voltages from the inverter stage 228 and/or the motor 208. For example, back electromotive force (BEMF) from the windings 212 of the motor may be measured or calculated. The control logic 200 may control the switches 250 and 254 using pulse-width modulation to apply varying voltages to the windings 212 of the motor 208. The switches 250 and 254 may generally be controlled inversely—that is, while switch 250-1 is turned on, switch 254-1 will be turned off, and vice versa.